Sound processing begins in ears, not in the brain

September 30, 2004|By William Hathaway, Tribune Newspapers: The Hartford Courant.

Scientists have long believed that sounds are translated within the brain, but new research suggests that the initial processing of sound starts within the ear itself.

In hearing tests of some 3,000 newborns, researchers at the University of California at Los Angeles and the University of Arizona found that the right and left ear amplify sounds differently, depending on the type of sound, according to a report in the current issue of the journal Science.

It's well established that the auditory regions of the two sides of the brain tend to specialize in sorting out sounds. The left side dominates in deciphering speech, for instance, while the right side of the brain takes the lead in processing tones and the sounds of music. The prevailing theory held that processing differences are due to structural differences within the brain's two halves.

"We always assumed that the left and right ears worked exactly the same way," said Yvonne Sininger, professor of head and neck surgery at UCLA and co-author of the study. "As a result, we tended to think it did not matter which ear was impaired in a person."

However, scientists found that tiny hairs called cilia in the left ear -- which because of neural wiring is most closely connected to the right side of the brain -- amplified music and tones more than cilia in the right ear. Conversely, cilia in the right ear -- which is connected neurologically to the left side of the brain -- provided extra amplification for rapid clicking sounds that mimicked speech.

"Even at birth, the ear is structured to distinguish between different types of sound and to send it to the right place in the brain," said Barbara Cone-Wesson, associate professor of speech and hearing sciences at Arizona.

The findings suggest that sound-processing programs for hearing devices need to be individualized for each ear to provide the best conditions for hearing speech or music, the authors said.